This invention relates to an endless belt used for power transmission to be used for a belt-type continuously variable transmission (CVT), especially to an endless belt for power transmitting, connecting link plates by pins.
One such endless belt for power transmitting has been developed by Van Doorne""s Transmissie (VDT) in the Netherlands (VDT; see, for example, Japanese Patent No. 1105154). The VDT belt has layered steel bands with metal V-shape blocks inserted therebetween, and power is transmitted by contact between the sides of the V-shape blocks and sheave faces of primary and secondary pulleys.
In this VDT belt, biting pitch and polygon variation can be reduced by making the V-shape block thinner, and the VDT belt is noiseless. But, the above-mentioned layered steel belt is made of high price material, and should be produced at high accuracy. Besides, in this steel belt, slip loss occurs between steel belt layers in power transmission.
In order to solve the above-mentioned problems, an endless belt for power transmission as shown in Japanese Kokai publication number H7-91498, for instance, has been proposed. As shown in FIG. 1, the metal belt is comprised of a plural number of first and second blocks 2, 3 located in a constant order in the longitudinal direction of a belt 1, a plural number of link plates 5 which connect these blocks through pins 6 which are divided into two pins (rocker pins) 6a, 6b, and spring means 7 stretching in the longitudinal direction of the link plate by engaging with these pins 6. This endless belt for power transmission has three open holes 9, 10, 9 formed in the first and second blocks 2, 3, and the link chain 11 is seated in these open holes 9, 10, 9. Since the pin 6 is engaged with the blocks 2, 3, the blocks 2, 3 and the link chain 11 are mutually connected to form an endless chain.
Projections 2a, 3a are formed so as to provide abutting surfaces between the first and the second blocks 2, 3 and, on the opposite sides of the blocks 2, 3 are slots 2b, 3b for receiving divided pins 6a, 6b. Within the first and second blocks 2, 3, the divided pins 6a and 6b are engaged with each other at their intermediate portions a, a and a predetermined clearance is formed at their outer end portions b, b. The pins 6a, 6b are engaged with the pin engagement slots 2b, 3b formed on the intermediate portions a, a so as to support each block 2, 3 with each block being free to oscillate with respect to the pins 6a, 6b. 
The outer side faces 2c, 3c of each block 2, 3 are inclined so as to adjust on the sheave side face of each pulley. Both outer end faces 6c of the pins 6 may be inclined for adjusting to the sheaves. The pin end face 6c has R form orthogonal to the longitudinal direction of the belt, such as Axe2x80x94A section, for instance, and can contact with the sheave face on a pitch circle of the belt.
In the present endless belt 1 for power transmitting, torque is transmitted in such a manner that the torque of a pulley unit is transmitted from the sheave side face by contact with the first and the second blocks 2, 3 and the pin 6, and tensile force acts on the link chain 11 comprising the link plates 5 through the pins 6.
In the above described metal endless belt 1, both side faces 2c, 3c of the first and the second blocks 2, 3 are formed in the shape of almost a straight line; however, they may be shaped as an arc in which case they contact the sheave side along a straight line by elastic deformation. As the belt 1 begins to curve by biting into the pulley, changing from the straight line travel, then, both side faces of each block can start to contact the sheave side at any position along its radial dimension. The contact start position in the longitudinal direction of the belt changes in accordance with the position of the block in the radial direction.
For this reason, the blocks may start to contact with the sheave at their upper portion or lower portion, as determined by the shape of the side surfaces of the blocks 2, 3, with respect to the X-axis, the Y-axis or the Z-axis (as shown in FIG. 1, the longitudinal direction of the belt is X-axis, the right and left direction is Z-axis, and the up and down direction is Y-axis) and/or by the deformation of the sheave side and the block. The contact start position of the blocks 2, 3 with the sheave in the longitudinal direction of the belt overlaps the pin 6. That is, the contact of the blocks 2, 3 with the sheave and the contact of the pin 6 with the sheave occur simultaneously.
In order to decrease undesired noise at the time of biting into the pulley by the metal endless belt 1, it is preferable to make the biting pitch (contact start position interval in the circumference direction) as small as possible, and to decrease the angle between the adjacent belt contact positions with respect to the pulley center, that is, polygon variation (polygon effects). But, when the position of start of contact of the block with the sheave overlaps the pin as mentioned before, the angle between adjacent contact points increases, shifting the angle to be originally held between the block and the pin. Then, the biting pitch is increased to that extent, and undesired noise is increased.
On the other hand, if the shape of the end faces of the divided pins 6a, 6b is a flat face along the side of the sheave or is the R shape with respect to the face orthogonal (radius direction) to the longitudinal direction of the belt, as in the above-mentioned prior art, above-mentioned (The R shape in the direction is the shape along the side of the sheave on the pitch circle, and is substantially the same as the above-mentioned flat face concerning the rotation of the pin at the time of biting), the relative clearance between the pin and the sheave is changed by the spin (rotation) of the pin when the belt bites into the pulley and the blocks and the divided pins are rotated to fit the effective diameter of the pulley. Then, the contact position between the pin and the sheave (in the circumferential direction and radial direction) is changed (change of the position where the pin starts to bite), and the above-mentioned polygon effects occur so as to cause undesired noise. At the same time, slip of the pin with respect to the sheave, especially the slip in the radial direction, increases.
Furthermore, by contacting the pin with the sheave at the position away from the rotational center of the pin, spin loss increases with the spin (rotation) of the pin. Besides, power loss occurs due to the change of the relative clearance between the pin and the sheave, especially by the slip in the radial direction, so as to reduce the power transmitting efficiency.
Thus, the first object of the present invention is to provide an endless belt for power transmission which is a tension-type belt using a link chain, having a high power transmitting capacity, which can be produced with relatively low cost, and having such a structure that the respective blocks and pins start to contact with the sheave side in order near the pitch line and the biting pitch into the sheave is made smaller so as to reduce noise.
The second object of the present invention is to provide an endless belt for power transmission, reducing the variation in pin width due to the rotation of the pin when the endless belt bites into the pulley so as to reduce undesired noise by the polygon effects and power loss by the spin of the pin.
The present invention provides an endless belt for power transmission having a plurality of divided pins (pin pairs) with rolling surfaces for abutting each other, a plurality of link plates comprising link chains alternately connected by said pins, and first and second blocks having projections capable of abutting each other, a concave slot provided on the side of each block, opposite the projection, for receiving one of the divided pins, and an open hole through which the link chain extends, front to rear, in the longitudinal direction. The divided pins have a shape and length such that both outer ends contact the sheave sides of a pulley. The first and second blocks have projecting outer side faces at positions approximately corresponding to the outer end faces of the divided pins and are shaped to contact the sheave sides of the pulley. Thus, the endless belt is structured so that a total of four parts, i.e., a pair of divided pins and the projecting outer side faces of the first and second blocks contact the sheave sides, in this order, in one pitch of the link chain.
The area of contact between the block and the sheave side is limited to within predetermined bounds near the pitch line corresponding to the position of the pin. Even if the sheave is bent or the block is inclined, a total of four parts, i.e., a pair of divided pins and the projecting outer end faces of the first and second blocks contact the sheave within one pitch of the link chain so as to make the biting pitch smaller and to decrease polygon effects. Therefore, in the endless belt for power transmitting, undesired noise can be decreased, although it is a tension-type chain comprising the link chains and blocks and having high power transmitting efficiency, and can be produced with relatively low cost.
Besides, even if the blocks are inclined with respect to the front and rear direction (in the longitudinal direction of the belt; the Z-axis), the variation of the effective block width due to the inclination is small, the load on the sheave is small, and adverse influence on the durability of the pulley and the block is reduced since the bounds of contact between the block and the sheave sides are restricted.
In one preferred embodiment of the present invention (see FIG. 7, for instance) the projecting outer end faces of the first and second blocks are formed in the shape of almost a straight line, having a predetermined inclined angle (they may alternatively be arced, and may contact the sheave side with elastic deformation) so as to match that of the sheave sides, are near the pitch line, and are shorter than the length in the radial dimension of the concave slot.
In another preferred embodiment of the invention, the projecting outer side face of the block is almost planar at an inclined angle predetermined to secure a contact area with the sheave side. In spite of this, the biting position of the block with respect to the pin can be correctly maintained.
In yet another embodiment (as shown in FIG. 9(B), for instance), the first and second blocks have concave slots for holding and contacting the divided pins on both of opposing sides facing longitudinally of the belt. These slots form an open hole therebetween.
In still another preferred embodiment, the concave slots for holding the pin and the projections contacting each other are formed at the opposing surfaces of the block facing longitudinally of the belt. Then, the length of the concave slot and that of the projection are set so as to improve bearing of load stress by the block. The length of the open hole extending between those opposing surfaces, and the number of the link plates of the link chain within the open hole are set so as to improve torque capacity and durability.
The divided pin is preferably located in the slot in a manner to develop a moment by contact with the concave slot to counteract a moment acting on said first and second blocks in contact with the sheave sides at their outer side face projections. Thus, the moment acting on each block in contact with the pulley is countered by the moment developed by the contact between the pin and the concave slot so as to resist change of position of the blocks.
Preferably, the position where the divided pin abuts the concave slot is located at a position shifted radially outward with respect to the pitch circle of the belt. In this manner, a moment is easily generated in a direction opposite to the moment acting between the block and the pulley.
Preferably, the outer end faces of the divided pin are formed curved in the longitudinal direction of the belt so as to contact the sheave side near the apical portion of the curved face. This prevents the top end side, in the belt running direction, of the outer side end face of the divided pin from first contacting with the sheave side so as to make the biting pitch bigger. In this manner noise is reduced.
Guide faces may be respectively formed on the open hole side of the block side portions, radially inward and outward of said concave slots, to abut the outermost sides of the link chain. Such guide faces allow the block to smoothly oscillate on the link plates, so noise is reduced.
Preferably, a stopper, for restricting the extent of relative rotation of the divided pin, is provided on opposing sides of the concave slot. Thus, the extent of rotation of the block with respect to the pin is held within predetermined bounds, and interference among the blocks can be reduced.
In one embodiment the outer end face of the divided pin is formed in the shape of a straight line having a predetermined inclined angle, as seen from said longitudinal direction of said belt. In this manner the end face of the divided pin and the sheave side can be smoothly contacted with each other.
In another preferred embodiment of the present invention, the end face of the pin has a curved shape at least in the X direction so that the variation of the pin length with rotation of the pin as the pin bites into the pulley is smaller, as compared with a pin having a flat end face or an end face curved in the Y direction, and the polygon effects are decreased. At the same time, lengthwise deformation of the pin and the sheave is decreased and their durability is improved. Further, slip between the pin and the sheave, especially slip in the radial direction and rotational slip (spin loss) are decreased, thereby decreasing power loss and improving power transmitting efficiency.
More preferably, the shape of the pin end face is almost cylindrical, having a curved shape in the X direction. Accordingly, two-dimensional grinding is sufficient to produce the pin end face, and its manufacture is simplified in comparison with the case where the pin end face is machined into a spherical shape and its machining efficiency can be improved. Furthermore, the influence on the effective length of the pin by the curved shape in the X direction is larger in comparison with a face curved in Y direction. Even if the pin end face is made cylindrical in the X direction only, there is no big influence on the noise of the belt in actual use or in power efficiency. Besides, by making the pin end face cylindrical, Hertz stress is reduced in comparison with a spherical shape.
Each pin is preferably a pair of divided pins having rolling surfaces abutting each other, so as to decrease power loss.
The end faces of the pin are preferably curved with a radius (Rp) of 5-15 mm. With the curved shape (R shape) having a radius of 5-15 mm, the strength with reduction of the above-mentioned Hertz stress can be maintained, and the variation of the length with the pin rotation is restricted within bounds compatible with belt efficiency.
More preferably, the end face of the divided pin has a displacement (xe2x80x9cdiscrepancyxe2x80x9d) (a, aA) of the center of radius (Rp) with respect to the rotational center (0) of the pin so that variation (xcex5) of effective pin length provides a clearance (xcex4) between the pin end face and the sheave in the X direction, which clearance is equally distributed to the positive rotational side and the negative rotational side of rotational angle (xcex8) in variation (xcex7a) of the rotational angle through which the pin rotates. Thus, the shape of the pin end face can be designed so as to make the variation of the pin length minimal, thereby providing a highly efficient endless belt, with decreased noise and power loss.
Most preferably, the discrepancy is from xe2x88x920.2 to +0.2 mm. Within the range of xe2x88x920.2 to +0.2 mm, the variation of the pin width can be restricted so as not to greatly influence the angle of the link plate of the divided pin.
However, the discrepancy should not be 0. When the discrepancy between the center of the radius (X coordinates) of the R shape of the pin end face with respect to the rotational center of the pin is 0, the variation of the pin length in the bounds of the change of the rotational angle of the pin is the maximum rotational angle of the pin (the same as the angle of the link plate of the pin) at the position where the belt starts to bite into the pulley, and is smaller in the rotational angle of the pin where the belt is rotated and the rotation of the pin finishes in the divided pin of the front side in the moving direction of the belt. As a result, the variation of the pin length is increased within the bounds of the change of the rotational angle of the pin. When the discrepancy does not include 0, that is, when the rotational center of the pin and the center of the radius (X coordinates) of the R shape of the pin end face do not correspond with each other, i.e., the shifted direction is on the positive or negative side with respect to Y axis for the center of the radius of the pulley, the variation of the pin width can be restricted to a smaller value within the bounds of the change of the rotational angle of the pin.
The divided pins extend through a sheet hole formed in the link plate with the side opposite the rolling surface abutting the link plate. A pair of divided pins seated within the link plate with a predetermined value (f; 5xc2x0, for instance) of positive rotation with respect to Y direction orthogonal to said X direction, with rotation in the moving direction of the endless belt being positive rotation. The leading half of the divided pin is preferably attached to the link plate at a predetermined rotational angle in the positive rotational direction. Then, when the endless belt bites into the pulley, the divided pin is rotated in the negative rotational direction, from the predetermined positive angular position it occupies, when the belt is in an almost straight line, to a predetermined angle of negative rotation upon finishing biting into the pulley. The rolling surfaces of the divided pin on both sides holding the center line is advantageous for strength.
Preferably, the center of the radius (Rp) of said R shape of the leading half of the divided pin is located a predetermined distance (xe2x80x9cdiscrepancyxe2x80x9d) (aA) to the trailing side of the rotational center (0) of the pin. In this manner, the variation of the pin length can be restricted to a small value within the rotational angle of the link plate relative to the divided pin.
Preferably, the radius of the R shape is almost 10 mm, and the predetermined discrepancy (ah) is almost 0.03 mm to provide an optimum shape for the pin end face. In practice, the minimum effective diameter of the pulley is about 28 mm and the maximum effective diamter of the pulley is about 69 mm in order that the variation of the pin length be kept at a minimum.
Preferably, the blocks have transverse projections at positions near the pitch line approximately corresponding to the end faces of the pin at both right and left outer side faces, and have a shape mating with the sheave sides (V) of the pulley.
Preferably the blocks consist of first and second blocks, having projections contacting each other in the X direction (running direction of belt) and a concave slot for receiving the divided pin on the opposite the projection. A total of four parts, i.e., the end faces of the pair of divided pins and the said projections of the side faces of the first and second blocks, contact the sheave sides, in this order, in one pitch of the link chain. In this manner, the biting pitch is made smaller, and polygon effects are decreased. Therefore, an endless belt having superior efficiency, decreased noise and improved durability, can be provided, even though a tension-type endless belt. Further, power transmitting efficiency is high and the belt can be manufactured at relatively low cost. Even if the sheave is bent or the respective blocks are inclined with respect to the X-axis, the Y-axis, or the Z-axis at the time of biting into the pulley, each block contacts the sheave side only on the side projections formed at predetermined positions near the pitch line (Pxe2x80x94P) and corresponding to the divided pin. Accordingly, the variation (C) in the block width (B) is smaller than with the conventional one.
On the contrary, the conventional blocks (2), (3) contact the sheave sides, over almost the whole radial length of the outer side faces (2c), (3c). Also, the width of the contacting area (t) of the block including the projection portions (2a), (3a) is wider. When the respective blocks (2), (3) are inclined (that is, with respect to the Z-axis) in the longitudinal direction X of the belt, as shown in FIG. 10(a), for instance, the wide contacting area (t) influences the variation A of the effective block width so that the variation becomes larger.
On the other hand, the divided pins are rotated, fitting the curve of the links with the biting of the endless belt into the pulley. The opposing end faces of the pin have a shape whereby the variation (xcex5) of the pin length (B) due to the rotation of the pin is small. Accordingly, the biting pitch of the pin end face into the sheave is maintained constant, the polygon effects are maintained small, noise is reduced, and the influence on the sheave by the rotational angle of the pin and the influence on the block are decreased so as to improve the durability of the belt-type continuously variable transmission. Moreover, the power transmitting efficiency is improved with the reduction in the spin loss of the pin.
The numerals and the marks which appear in parenthesis in this description are for convenience in reference to the drawings and are not intended to influence the scope of the present invention, as defined by the appended claims.